1. Field of the Invention
The invention relates to a method and apparatus for disc rotation control in an optical storage system, more particularly to a method and apparatus for disc rotation control in an optical storage system based on detected extent of disc warping.
2. Description of the Related Art
An optical disc is prone to warp due to numerous factors, such as manufacturing errors, prolonged exposure to humidity or sunlight, applied forces or pressure, etc. As shown in FIG. 1, when loaded on a tray 40 of an optical storage system, a warped optical disc 2 will not lie flat on the tray 40. Hence, due to positional imbalance of the optical disc 2 relative to a rotary axis thereof, a lot of noise and vibrations will be generated during high-speed rotation of the optical disc 2. As a result, the service lives of a spindle motor and the associated servo mechanism of the optical storage system are shortened, and stability of disc recording and playback operations are adversely affected. Moreover, manufacturers are mandated to produce optical storage systems that comply with specified allowable noise and vibration levels during disc recording and playback operations.
In co-pending U.S. patent application Ser. No. 10/889,736, filed on Jul. 13, 2004, the applicants disclosed a digital signal processing device for disc rotation control in an optical storage system, which is capable of generating a focusing error signal from light that was reflected by an optical disc loaded in the optical storage system. The digital signal processing device includes a low pass filter for removing a high-frequency component of the focusing error signal to obtain a filtered signal, a direct current level remover for removing a direct current component of the filtered signal to obtain a warp-indicating signal, and a controller for comparing the warp-indicating signal with a predetermined threshold value to determine extent of warping of the optical disc. The controller functions to control the optical storage system so as to limit maximum rotation speed of the optical disc according to result of the comparison made by the controller.
The entire disclosure of the aforesaid co-pending U.S. Patent application is incorporated herein by reference.